Configure check for system "rw" library

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This has no dependencies and is easy enough to check for, so we should do it.

Component: **build: configure**

Author: **Michael Orlitzky**

Branch/Commit: **[`395a185`](https://github.com/sagemath/sagetrac-mirror/commit/395a1859198309a2802a20fe91eddf8fac13acda)**

Reviewer: **Dima Pasechnik**

_Issue created by migration from https://trac.sagemath.org/ticket/27814_

